Granulocytic sarcoma presenting as a mediastinal tumor. Report of a case and cytological and cytochemical studies of tumor cells in vivo and in vitro.

An unusual case of granulocytic sarcoma in a 23-year-old man is reported. The patient initially presented with mediastinal tumor and was diagnosed clinically as having thymoma. The patient was treated by radiotherapy and surgical removal of the tumor. Histology of the excised tumor had been nondiagnostic because of extensive fibrous changes. Eight months later, the patient developed pleural effusion on the right, which soon was followed by blood and bone marrow pictures consistent with acute promyelocytic leukemia. In vitro culture of pleural effusion cells unexpectedly gave rise to a continuously growing peroxidase-positive myeloid cell line. Autopsy revealed the recurrent mediastinal tumor to be positive for intracytoplasmic naphthol AS-D chloroacetate esterase and lysozyme activity. From these findings, the patient retrospectively was diagnosed as having mediastinal granulocytic sarcoma, which terminated in pleural effusion and acute promyelocytic leukemia.